1. Field of the Invention
The present invention relates to a keyboard device, and more particularly, to a keyboard device having terminals connectable to peripheral devices other than a computer main body.
2. Description of the Related Art
Conventionally, personal computers and their peripheral devices have been developed for the purpose of reduction of manufacturing cost and simplification of configuration. Especially, a keyboard device, connected as an input device to a personal computer main body, has a keyboard main body with a large number of key switches, a case accommodating the keyboard main body in a state where the key tops on the key switches are exposed, and a circuit board, included in the case, having a control circuit to control electric signals transferred between the keyboard main body and the personal computer main body. As the large number of parts of the keyboard device are manufactured and assembled at a high cost, cost reduction measures are always required.
In recent years, a keyboard device, connected to a personal computer main body, which further has terminals commonly connectable to various peripheral devices such as a mouse, has been provided. In the conventional system, generally, peripheral devices such as a keyboard, a mouse and a printer are respectively connected to specialized ports for the respective peripheral devices of the personal computer main body. On the other hand, in the system having the above keyboard device, the keyboard device is connected to the personal computer main body, and peripheral devices such as a mouse and a printer can be connected to peripheral-device common connection terminals provided in the keyboard device. For such connection, a connector in which a plug of the peripheral device is inserted is provided on a control circuit board in the keyboard device. The formats of the plug, connector and the like for this sort of connection are standardized as USB standards, and attract attention as USB-compliant peripheral devices.
In use of personal computer, input devices such as a keyboard and a mouse are always manipulated by a user, and build up a large amount of static electricity. The electrostatic buildup occasionally causes electric discharge adversely affecting, as noise, various signals transferred between the personal computer main body and the input devices.
Different from the conventional system where the input devices are connected to the specialized ports of the personal computer main body in parallel, in the above USB-compliant system, if the mouse is connected on the downstream side of the keyboard, as well as a data signal from the mouse, an address signal, for recognition of the presence of downstream input device i.e. the mouse by the personal computer main body, is always transmitted inside the keyboard. In the conventional system, even if static noise enters and causes abnormality in data signals, normal operation can be restored without any particular problem after reset and retransmission of data. However, in case of the USB-compliant system, upon entrance of noise, if the address signal of the mouse is reset, the personal computer main body cannot recognize the presence of the mouse regardless of connection of the mouse downstream of the keyboard. In this case, there is a possibility that the operation by using the mouse cannot be made. From this situation, especially in a USB-compliant keyboard, improved static-noise resistance is required, and antistatic measures are urgent matters.
Further, upon prescription of static-noise countermeasures, to avoid an increase in the manufacturing cost of the keyboard device, it is desirable to take measures against static noise by a method as simple as possible without high cost.
The present invention has been made to solve the above problem and has its object to provide a USB-compliant keyboard device capable of preventing malfunction and operation failure due to static noise by a simple method.
According to one aspect of the present invention, the foregoing object is attained by providing a keyboard device comprising: a keyboard main body having plural key tops on its upper surface; a case accommodating the keyboard main body; a control circuit board on which a control circuit that controls the keyboard main body is mounted; a peripheral-device common connector (hereinbelow referred to as a xe2x80x9cUSB connectorxe2x80x9d) connected to the control circuit board; and a conductive plate covering the control circuit board from a lower position.
Further, it is preferable that in the keyboard device having the conductive plate, the conductive plate is electrically connected to a ground terminal on the USB connector side on the control circuit board, and is electrically connected to a ground terminal on the computer main body side on the control circuit board. Otherwise, if the conductive plate cannot be directly connected to the ground terminals without difficulty for structural or other reasons, the conductive plate may be electrically connected around the ground terminal on the USB connector side on the control circuit board and electrically connected around the ground terminal on the computer main body side on the control circuit board.
The present inventor has paid attention to two factors of static noise entrance to the keyboard device, radiation from a surface of a desk, platform or the like on which the device is placed, and electrical conduction from the USB connector for connection with peripheral devices such as a mouse. In the keyboard device of the present invention, as the conductive plate provided to cover the control circuit board from a lower position functions as a shield plate, the static noise radiated from the surface of the desk can be shielded by the conductive plate. As a result, the probability of occurrence of operation failure due to static noise adversely effecting signals on the control circuit board can be sufficiently reduced.
Further, in a case where the conductive plate is electrically connected to the ground terminal on the USB connector side on the control circuit board and the ground terminal on the computer main body side on the control circuit board, respectively, as the conductive plate dissipates the static electricity, and the static electricity entered through the USB connector flows from the ground terminal on the USB connector side through the conductive plate, to the ground portion of the computer main body from the ground terminal on the computer main body side. That is, as the static electricity entered from the USB connector instantaneously passes through the conductive plate, the probability of occurrence of operation failure due to static noise adversely effecting signals on the control circuit board can be sufficiently reduced.
Note that generally, the control circuit board is constituted with a print circuit board, and wiring as an escape route for static electricity is formed so as to connect the ground terminal on the USB connector side to the ground terminal on the computer main body side, on the circuit board. Accordingly, even in a case where the conductive plate is connected to the control circuit board, static electricity flows not only through the conductive plate but also through the electrostatic conductive wiring on the control circuit board. However, since the impedance of the conductive plate is lower than that of the wiring, the amount of static electricity which flows through the conductive plate is far larger than that of static electricity which flows through the wiring. Accordingly, the keyboard device of the present invention having the conductive plate can obtain the above advantage.
Further, even if both ends of the conductive plate are not directly connected to the ground terminals on the USB connector side and the computer main body side, as long as they are electrically connected around the respective ground terminals, the conductive plate can function as an escape route for static electricity. Thus an advantage similar to that described above can be obtained.
In the keyboard device of the present invention, as a particular method for electrically connecting one end of the conductive plate to the ground terminal on the USB connector side, the one end of the conductive plate may be inserted between an arbitrary member such as a case and the USB connector, so that the end is pressed into contact with the ground terminal. Otherwise, the one end of the conductive plate may be soldered to the ground terminal itself of the USB connector or a land around the ground terminal on the control circuit board.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.